Portable incubator



7 July 5, 1960 w. w. KENYQN, 2,944,134

' PORTABLE INCUBATOR Filed June 24. 195.8 2 Sheets-Sheet 1 INVENTOR. WALTER W. KENYON ATTORNEYS July 5, 1960 w. w. KENYQN PORTABLE INCUBATOR 2 Sheets-Sheet 2 Filed June 24, 1958 INVENTOR WALTER W. KENYON \M,9ow7 I- W ATTORNEYS United States Patent M I I I PORTABLE INCUBATOR I Walter W. Kenyon, Needham, Mass., assignor to Millipore Filter Corporation, Watertown, Mass, :1 corporation of Massachusetts Filed June 24, 1958, Ser. No. 744,228

4 Claims. (Cl. 219-20 This invention relates to incubators and provides an electrically heated apparatus for incubating bacteriological specimens, which-is light weight and portable and which may be operated on any of several voltages. The

apparatus may accordingly be used in numerous locations without being dependent on the availability of one particular source of power.

In incubating bacteriological specimens it is important that the temperature variation be kept at an absolute minimum. In the design of these units it is advantageous to utilize resistance elements as the source of heat, since they are light, eflicient and easily controlled. Preferably the resistance windings are so located with reference to the geometry of the incubation chamber as to provide uniform heating throughout the chamber. A unit employing a resistance winding and designed to operate on any of numerous voltages requires some arrangementfor modifying the circuit so that the same amount of heating is provided regardless of the voltage applied. The present invention provides not only for modification of the circuit of the resistance windings but also provides for absolutely uniform distribution of power along the I length of the winding in a most efiicient manner.

The incubator of this invention includes in general an outer housing within which is situated an inner incubator compartment arranged to receive specimens to be cultured. Heating of the compartment is provided by two courses of resistance windings which are evenly distributed about the vertical walls of the compartment.

One of the windings by its greater length is of relatively high resistance and the other of relatively low resistance and they are connected so that any of several voltages may be connected to them in such a manner that at any voltage the power consumption is the same and the heating is uniformly distributed along the length of the windings. The windings are connected together, in series, and terminals for power connections are provided at the extreme endsof the windings, at a point-where the windings connect together, and at the resistance mid-point,

that is, the point where the total resistance on one side of the-terminal is equal to the total resistance on the other side;- A switch in the power winding circuit provides theconnections necessary for any given voltage source.- An additional range of useful voltages is provided by including a transformer through which high A.C. voltages may be reduced to one of the lower voltages at which the system is designed to operate.

I 2,944,134 Patented July 5, 1960 Fig. 4 shows diagrammatically the switching arrangement by which the various circuits are provided.

In the preferred embodiment of this invention, as shown in Fig. 1, the incubator is generally organized about an outer casing 10 having a hinged cover 12. The casing 10 is enclosed at its top by a panel 14 on which is mounted a temperature control knob 15 and a voltage selector knob 16, which connect respectively to a thermostatic switch 18 and a S-deck S-position rotary switch 20.

The incubator compartment 24 extends inwardly from the panel 14, and may conveniently be formed as a part of the panel. In form the compartment 24 is generally rectangular and of dimensions suitable for receiving a rack on which culture dishes may be placed. The compartment is conveniently provided with a transparent cover 26 which may be hinged to the panel 14.

A thermostatic switch 18 is. mounted in the wall of the compartment 24 with its 'temperature sensing part exposed to the interior of the compartment, and a flexible cable 28 connects the switch with a temperature control knob 15 through which the thermostatic setting of the switch may be varied. The thermostatic switch 18 is typically of the snap action bellows type commercially available. 7

Electrical heating of the compartment is provided by two courses of resistance windings, a high resistance winding 30 and a low resistance winding 32, each of which is evenly wrapped around the sidewalls of the incubator compartment 24. These are surrounded by a layer of insulation 21. Circuits to the windings 30 and 32 are provided through the S-deck S-position rotary switch 20' in such a manner that the combined power ratings. of the windings is always the same and that the heat is genera-ted uniformly along the course of the windings. I

The unit illustrated is also designed to operate on high voltage alternating current sources, for which purpose there is provided a transformer 34 through which the voltages are reduced to those for which the windings are designed. A power connection receptacle 36 at the side of the casing 10. provides for the connection of the unit to a suitable power source. I

By way of illustration, a typical embodiment of the unit may be designed to operate on 220 volts A.C., 110 volts A.C.,24 volts A.C. or D.C., 12 volts A.C. or DC. and 6 volts A.C. or D.C. The resistance windings are arranged so that 24 volts, 12 volts, or 6 volts can be supplied to them to give the same power consumption and an even distribution of power. Whenoperating at 220 volts A.C. or 110 volts A.C., the power is supplied to the primary of the transformer 34, and through it the secondary voltage which is applied to the resistance windings, is reduced to 24 volts or 12 volts respectively.

The arrangement of the resistance windings 30and 32 is shown diagrammatically in Fig. 2, and the circuits to them at the several voltages are shown in Fig. 3. The

two windings are connected together and power terminals are provided at the extreme ends, A and D (Fig. 2) at the juncture of the two windings, C, and at the resistance midpoint B, where the resistance on one side R equals the total resistance series on the other side R +R At24'volts, power is supplied through the end termi- .nals A and D, with the windings being in series and'the total resistance of them equals R +R +R I At 12 volts, one of the power leads connects with both terminals A and D and the other connects with B, with R thus being in parallel with R and R .Since the same current flows in each branch of the parallel circuit and the total resistance is one quarter the sum 3 of R -l-R -i-R The power consumption is accordingly the same and is uniformly distributed.

At 6 volts one of the power leads connects with terminals A and D and the other connects at terminal C so that R is in parallel with R +R The resistance value of R is such that the power consumption at 6 volts will be the same as at 12 and 24 volts, that is to say, the resistance of the parallel circuit will be one-sixteenth the sum of R -l-R -l-R From the nature of the circuit it will be seen that the heating will be uniformly distributed along the length of the windings.

-By way of example, a unit designed to operate at 40 watts power, at voltages of 24, 12 and 6, will require the following resistances:

As shown in Figs. 3a and 3b the circuits employed for use with power sources of 220 and 110 volts are essentially the same as those employed at 24- volts and 12 volts respectively with the exception that the power source connects with the primary 'of the transformer while the resistance windings are energized from the secondary. The transformer will accordingly be rated at 220/24 or 110/12 (reference to the ratio of primary/secondary voltages) to provide for the proper voltage reduction.

A suitable switching arrangement for providing the desired circuits at the several voltages is shown diagrammatically in Fig. 4. The various connections are made by means of a S-deck 5-position switch 20, the decks of which are ganged together through a control shaft which connects with the voltage selector knob 16. At the 220 volt setting the pole of each of the 5 decks is at the position designated 1 in Fig. 4;

At the 110 volt setting each pole is at the terminal designated 2;

At the 24 volt setting each pole is at the terminal designated 3;

At the 12 volt setting each pole is at the terminal designated 4, and

At the 6 volt setting each pole is at the terminal designated 5.

Referring to the individual decks by Roman-numeral designations I, II, III, IV and V, followed by an Arabic numeral designation of the terminals, the followingcircuits can be traced for the various settings:

For 220 v.: From power lead 40 to I-1 to transformer primary to thermostatic switch 18 to power lead 42. Secondary circuit: from transformer secondary to lead 44 to III-1 to R to R to R to lead 45 to secondary.

For 110 v.: From power lead 40' to I-2 to transformer primary to thermostatic switch 18 to power lead 42. Secondary circuit: from transformer secondary to lead 44 to III-2 to parallel circuit, one branch being R to IV-Z to lead 46 and the other being R and R said branches joining at 45, to transformer secondary.

For 24 v.: From power lead 40 to II3 to lead 44 to III-3 to R to R to R to lead 45 to V 3 to thermostatic switch 18 to power lead 42.

For 12 v.: From power lead 40 to H4 to lead 44 to III-4 to a parallel circuit, one branch being R to IV-4 to lead 46 and the other branch being R and R said branches joining at 45, to V'4 to thermostatic switch 18 to power lead 42.

For 6 v.: From power lead 40 to II-5 to lead 44 to III-5 to a parallel circuit, one branch being R to R, to IV-S to lead 46 and the other branch being R said branches joining at lead 45, to V-S to thermostatic switch 18 to power lead 42.

The preferred circuit also includes a fuse 45 in the lead 44 to protect the power windings and a lamp 47,. of 12 v. rating, connected in parallel with R and R to; show when the power is on. A

Although this invention has been described in detail with reference to its preferred embodiment, it is contemplated that modifications will readily occur to those skilled in the art familiar with this description, and that such may be made without departing from the scope of this invention.

Having thus disclosed my invention and described in detail a preferred embodiment thereof, I claim and desire to secure by Letters Patent: 7

1. An electrically heated incubator operable on any one of several voltages comprising an outer housing, partitioning means forming an inner compartment within said housing, a radiant heating zone surrounding said compartment including at least two resistance windings surrounding said inner compartment connected together in series to form a series resistance, one of said resistance windings being of greater resistance than the other and including an intermediate point where said series resistance is divided-in half, each of said windings being coextensive with and evenly distributed along the length of, 7

said zone, power connections to said windings including one at each end of said series resistance, one where the windings connect together, and one at the said inter.- mediate point, a pair of power leads, and switching means for selectively connecting said power leads to said power connections in such a manner that current passes through the whole length of each of said windings regardless of which power connections are selected, and a thermostatic switch responsive to the temperature in said compartment in said power leads.

2. An electrically heated incubator operable on 6, 12 or 24 volts comprising an outer housing, partitioningmeans forming an inner compartment within said housing, a radiant heating zone surrounding said compartment includ; ing two resistance windings connected together in series to form a series resistance, one being'of greater resistance than the other and including an intermediate point where said series resistance is divided in half, each of said windings being coextensive with and evenly distributed along the length of said zone, power connections to said windings including one at each end of said series resistance, one where the windings connect together, and one at the said intermediate point, a pair of power leads, and switching means adapted at one position to connect the power leads to the connections at the ends of said series resistance, at one position to connect one power lead with both connections at the ends of said series resistance and the other power lead to the power connection at said point on said winding of greater resistance where said series resistance is halved, and at one position to connect one power lead with both connections at the ends of said series resistance and the other power lead tothe power connection where the windings connect together, whereby" said leads are connected in such a manner that current passes through the whole length of both of said windings regardless of which power connections are selected, and

a thermostatic switch responsive to the temperature in said ,comportment in said power leads.

3. An electrically heated incubator operable on 6, 12 1 24, or 220 volts comprising an outer housing, and partitioning means forming an inner compartment; a radiant heating zone surrounding said compartment including two courses of resistance windings,.one beingzof greater resistance than the other and including an'inter-p mediate point where said series resistance is divided in half, connected together in series to form a series resist ance, said windings being coextensive with and evenly distributed along the length of said zone; power connections to said windings including one at each end of said series resistance, one where the windings connect together,

and one at the said intermediate point; a pair of power leads; a transformer; and switching means adapted at one position to connectin series the power leads to the connections at the ends of said series resistance, at one position to connect in parallelone power lead with both connections at the ends of said series resistance and the other power lead to the power connections at the point on said winding of greater resistance where said series resistance is halved, at one position to connect in parallel one power lead with both connections at the ends of said series resistance and the other power lead to the power connection where the windings connect together, at one position to connect the said transformer in circuit and to further connect in series the power leads of the secondary side of the said transformer to the connections at the ends of said series resistance, at one position to connect the said transformer in circuit and to further connect in parallel one of the power leads of the secondary side of the said transformer with both connections at the ends of said series resistance and the other power lead of the secondary side of the said transformer to the power connection at the point on said winding of greater resistance where iaid series resistance is halved, whereby said leads are connected in such a manner that current passes through the whole length of each of said windings regardless of which power connections are selected; and a thermostatic switch responsive to the temperature in said compartment in said power leads.

4. An electrically heated incubator operable on any of Several voltages comprising an outer housing, partition- 6 ing means forming an inner compartment with said housing, a radiant heating zone surrounding said compartment including at least two resistance windings surrounding said inner compartment, one of said resistance windings being of greater resistance than the other, each of said windings being co-extensive with and evenly distributed the length of said zone, power connections to said windings including one at each end of said series resistance, one where one winding joins the other, and one at the said intermediate point, a transformer, a pair of power leads, and switching means for selectively connecting said power leads to said power connections and to said transformer such that said leads are connected in a manner that current passes through the whole length of each of said windings regardless of which power connection is selectmi, and a thermostatic switch responsive to the temperature in said compartment in said power leads.

References Cited in the file of this patent UNITED STATES PATENTS 1,721,582 Ziola July 23, 1929 1,979,222 Goodwin Oct. 30, 1934 2,065,760 Smith Dec. 29, 1936 2,584,435 Doerr Feb. 5, 1952 2,622,183 Rosenthal Dec. 16, 1952 

